Gemini Changes

Ensuring the system responds to the rapid evolution of the GB gas market.

Scheduled Gemini Changes

There are two scheduled changes currently being implemented, details are as follows:

Mandatory Setting of Auction Bid Parameters – UNC Modification 0745

Background click here to view the Change Pack

There have been several instances of incorrect prices and/or capacity values entered by Users during the bid capture process for short term capacity auctions in both Gemini and Gemini Exit.

These bid errors have impacted on other auction participants (via invoicing) due to neutrality processing. There is also increased potential for application of higher overrun charges at sites where bid errors have occurred.

The purpose of the Change

The Change is to reduce the risk of Users making bid submission errors by mandating the use of User and/or Shipper Preferences allowing for Bid Validation to be put into place prior to bid capture/requests.

The requirements as specified in approved Uniform Network Code (Modification 0745) will make the setting of the existing bid parameter function mandatory in the Gemini System.

Users must first set up User/Shipper preferences for the Validation Parameters – Bid Price and Bid Capacity for all relevant locations and short-term auctions before placing the bids/requests

The change only applies to the below short-term auction Methods of Sale (MoS) and will become effective 1 October 2021

Gemini Entry Gemini Exit

Useful Information

MOD745 External Screens Pack v1.0

Last updated on 23 Aug 2021


Delivery of Modification 0728B – Conditional Discount for Avoiding Inefficient Bypass of the NTS

On 27th April 2021 OFGEM made the decision to implement MOD0728B. This change will introduce a new Conditional Discount to the Charging Framework so that a product to manage potential inefficient bypass will be in place from 01 October 2021.

If you have any questions or concerns relating to this change please contact Matthew Rider


On Tuesday 7th September we are holding an awareness session dedicated to MOD0728B where we will be walking through the material and answering any questions. To register for this session please click on the following link:

Change Awareness Session - XRN 5093 & XRN 5341 Tickets, Tue 7 Sep 2021 at 10:00 | Eventbrite

Useful Information

Change Pack (which includes the design description and solution): Extraordinary Change Pack May 2021

Awareness material:

Details of MOD0728B:


Gemini Changes Delivered

CP4550 – Gemini Re-Platform

The Gemini system is built on ageing equipment, with a 2017 health assessment recommending a new platform on new hardware.

Download the CP4550 Change Proposal from the Joint Office of Gas Transporters website.

The project will relocate the Gemini system to new equipment.

We will be working with NG to understand the:

  • key requirements for hosting the Gemini system
  • potential impacts to customers and interfacing systems

This project will be implemented after the GB Charging changes (CP4376) in 2020.

CP4376 – GB Charging and Incremental (IP PARCA)

This is a large project, with a key element being the delivery of changes from the Great Britain Charging Review.

This is a significant change to how National Grid Gas Transmission (NGGT) will receive its revenue.

The change is also likely to impact future UK Link releases.

Download the CP4376 Change Proposal from the Joint Office of Gas Transporters website.

The CP4376 project has been split into two parts - A and B.

Part A – CP4376

Part A was implemented in November 2018.

Part B – CP4376

The majority of the changes are included in Part B with the Analysis and Design phase which started in May 2018.

Full implementation is expected in September 2019. 

A number of components will be effective from 01/10/2020 and details of these can be obtained from the Gemini Projects team.

CP4368 – EU Gas Capacity Conversion Change – February and March 2018

The Capacity Allocation Mechanism (CAM) code requires a capacity conversion mechanism to be offered to Users at Interconnection Points (IPs). Modification ‘616 Capacity Conversion mechanism for Interconnection Points’, introduces this requirement to the Uniform Network Code (UNC).

The introduction of the conversion mechanism risked unfair competition. With the processing of the mechanism, shippers who were matching unbundled capacity on either side of the IP would also need to have purchased bundled capacity because of prioritisation restrictions.

To ensure fairness, the existing buyback functionality of Gemini can now be used. By using the facility and introducing a new manual process by NG, it ensures compliance with the EU obligation and a level playing field for all Users.

Download the CP4368 Change Proposal from the Joint Office of Gas Transporters website.

The change was made live on 18th February 2018.

A new Entry Method of Sale has been introduced to support the change. Two new charge types have been created on the NTS Entry invoice:

  • CEC Capacity Conversion Entry Charge
  • CEA Capacity Conversion Entry Adjustment

These charge types were effective from 1st March 2018.

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